Fused joint



March 26, 1940.

w. DALLENBACH FUSED JOINT Filed Dec. 13, 1937 Patented Mar. 26, 1940 raiarsss 5. ruse .9M

whitewater saun'.ehflmatuagleeri I ,;-/assignor,;to ;Juliuslintschgliommandita lia g pl w necemberlfa', 1937, Serial-N f applianceduring working or dunng'prepsrauon for work-,

ing to temperatures of the' order of magnitude .of severalhundredfdeg're'eslj According to the'inyenticn sucha fused'joint is madeby providing 'ontlie edge of the metal part to be joined to the ceramicbody an excess of material which prevents the pressure stresses at thejoint from being converted into tension stresses along the axialextension of the adhering surface.

This is preferably effected either by prolonging the edge of the metalpart beyond the adhering surface or by providing it with a rim in aradial direction; in some circumstances both expedients may be usedtogether.

The invention is illustrated by the accompanying drawing, of which:

Figure l is a longitudinal section of a part of an electrode leading-intube, for example for vacuum discharge apparatus, by means of which willbe explained the changes of form of the metal parts to which theinvention relates;

Figures 2, 3 and 4 show constructional examples of the invention, and,in fact, represent parts of electrode leading-in devices for currentrectifiers.

In Figure 1, l indicates a part of the envelope of a metal vacuumvessel, for example a mercuryvapour rectifier, into which there is to beinsert ed from above a ceramic tube 2, in particular a steatite tube,which serves for the reception of the lead of an electrode. This ceramictube 2 is connected in a vacuum-tight manner with an annular part 3consisting of a metal sheet of suitable composition, for example ofalloys of nickel, chromium, vanadium, with iron, or chromiumnickelalloys, the adhering surface 4 formed by an annular projection 5 of thetube 2 being fused to the flange l of the annular part 3 by means of aninterposed mass of glass or enamel flux 6 (hereinafter called glassflux). Instead of an enamel flux there may be used a burning or firingor vitrifying process; The annular part 3 is finally welded to the welli of the vessel at 12.

The heat-expansion cc-eflicients of the ceramic body, the flux, and themetal part 3 are in this case so related that the ceramic body and theflux have as nearly as possible equal co-eflio qa'sas l cients' ofexpansion, whilstthat'of the "metal part is somewhat-greater in ordertoproduce a contractionthat'increas'es' the strength of the con- Now ithas been found that in such a case there is the danger thatcleformationof the annular flange' l resulting from the contraction stress may giverise' to tensicn'stresses in the adhering surface. 'Such'tensionstresses'in the adheringsurface-are to be feared particularly when theadhering surface comparatively short in the axial direction incomparison with the diameter at the joint, which; on the other hand, isfavourable as regards possible thrust stresses.

Now, by the contraction that occurs and the tension stresses possiblyarising therefrom, the flange! is deformed conically in the way shown inthe right-hand portion of Figure l. The generatrix of the peripheralsurface here makes an angle o with the axis of the tube. This is to beattributed to the fact that in consequence of the shortness of the axiallength of the adhering surface there is at the lower end of the flange1, (inasmuch as this end, as is usual, is flush with the annularprojection 5) not suflicient material to contract the lower portion ofthe flange 1 with sufficient force upon the annular projection 5. Nowthis conical deformation of the flange I has the result that ,at thelower end of the flange f the fused joint between the metal, the glass,and the ceramic body begins to open, and in fact generally in the glass.This is apt to cause a leak, or at least a considerable weakening of thejoint.

Now if the metal flange I is in accordance with the invention prolongedbeyond the annular projection, as is shown in the left-hand side ofFigure 1, the deformation of the flange I exhibits itself as abarrel-shaped arching of the flange, and the middle tangent of thedeformed flange I remaining parallel to the axis of the tube, so that nodangerous tension stresses can occur at the adhering surface (therepresentation in Figure l is of course exaggerated).

Figure 2 shows an example of a joint in which according to the inventionthe anular flange 1 is prolonged beyond the annular projection 5.

It is however not necessary to produce the advantageous barrel-likedeformation of the flange I by prolongation of the flange, but, as shownin Figure 3 the flange I may be rimmed radially. In consequence of therim 8 thus produced there is then, notwithstanding the flush terminationof the flange l and the annular projection 5, sufficient material toprevent the coni a high-vacuum vessel with a metalwall, The distributionof the metal should always be so cal deformation of the flange 1represented in the right-hand portion of Figure 1.

In the case of the example represented in Figure 4, instead of theceramic tube 2, a ceramic disc 9 which is to be regarded as at the levelof the annular projection 5 is to be fused, with interposition of a flux6 to a cylindrical tubular part "L"; which widens" out for example"slightly in an upward direction. The securing of the necessary excessof material at the joint is effected by a prolongation of the tubularpart III. Instead of this, however, a rim may be used;

The tubular part is then welded to a wider the ceramic-insulator issmaller than the diameter of such extension.

the constructional examples here given, butmay tube H. L; e

The invention is of coursd'not restrictedto be used also in similarcases,-;- in particular: for

chosen that the metal part will be pressed over its entire(adheringsurface upon. its {ceramic support. and conversion ;,of thepressure stress into tension stress ,along the axial, extension of theadhering surface cannot occur. What 1130 3x 75); the a v3 1.,

1. An electrodeplq dri for-vacuum discharge apparatus, comprising a;wall -,forming the envelopeof the apparatus, a metal part connectedtosaid wall, a tubularmeramicinsulator to ac-. commodate the currentsupplying conductor, said insulator hayingon its outer surfacean annular-extension,;the,metal part havingan annular terminal surrounding theannular exten' sion of the insulator and joined vacuum-tight to saidextension by shrinking and by fusion, said terminal extending in bothdirections beyond the annular extension of the insulator and clear ofthe insulator in such extension.

2. An electrode lead-in according to claim 1, wherein the vacuum-tightjoint between the metal part and the extension of the ceramic in- Isulator are connected by the employment of a "melting flux.

electrode lead-in according to claim I,

wherein the axial dimension of the projection of 4An electrode lead-infor vacuum discharge apparatus, comprising a wall forming the envelopeof the apparatus, a metal both extending therefrom, a tubular insulatorof ceramic material to accommodate a conductor to an elec-

